J. Limnol., 2013; 72(1): 35-51 DOI: 10.4081/jlimnol.2013.e4 Recent findings regarding non-native or poorly known diatom taxa in north-western Italian rivers Elisa FALASCO,* Francesca BONA Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy. *Corresponding author:
[email protected] ABSTRACT Diatoms of the major rivers of North-Western Italy were investigated to highlight the presence of species of particular ecological in- terest but not as yet recorded. The survey area included streams belonging to seven different hydroecoregions (HERs) with a wide range of physical characteristics. Between 2008 and 2010, 200 samples were taken for the study of the diatom community composition, while a larger set of samples was examined to determine the presence or absence of the nuisance diatom species Didymosphenia geminata (Lyngbye) Schmidt. A specific field study was performed in two rivers characterized by persistent blooms of this species to evaluate the effects of its proliferation on the benthic communities. D. geminata was present in almost 20% of the samples. From a comparison with published data, we can confirm that D. geminata has recently been expanding its ecological range, as it has been found also in mesotrophic lowlands water. In some instances the formation of massive proliferation has been recorded. The calculation of autecological values confirmed its preference for oligotrophic waters with low mineral content and organic loading,use although with a wider ecological amplitude than recorded in the first studies on this species. Another four taxa of particular interest were detected: Achnanthidium subhudsonis (Hustedt) Kobayasi (in 15 sites), Cymbella tropica Krammer (11 sites), Mayamaea cahabaensis Morales and Manoylov (2 sites) and Reimeria uniseriata Sala, Guerrero and Ferrario (18 sites).